Effects of FDM-3D printing parameters on mechanical properties and microstructure of CF/PEEK and GF/PEEK

Fused deposition modeling (FDM) has unique advantages in the rapid prototyping of thermoplastics which have been developed in diverse fields. However, although great efforts have been made to optimize FDM process, the mechanical properties of printed parts are limited by the weak interlamination bonding as well as the poor performance of raw filaments used, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA). Adding fibers into thermoplastic matrix and preparing high-performance filaments have been indicated to enhance the properties of fabricated parts. Recently, heat-resistant polyetheretherketone (PEEK) and its fiber reinforced composites were proposed for FDM process due to overcoming the limitation of equipment and process. However, few researches have been reported on the effects of FDM-3D printing parameters on the mechanical properties of fiber reinforced PEEK composites. Therefore, 5wt% carbon fiber (CF) and glass fiber (GF) reinforced PEEK composite filaments were prepared respectively in this study. The effects of various printing parameters including nozzle temperature, platform temperature, printing speed and layer thickness on the mechanical properties (including tensile strength, flexural strength and impact strength) were surveyed. To analyze the microstructure and failure reasons of printed CF/PEEK and GF/PEEK samples, the tensile fractured surfaces were investigated via scanning electron microscope (SEM).     

Effect of beam current on microstructures and mechanical properties of joints of TZM/30CrMnSiA by electron beam welding

Electron beam welding experiments of TZM alloy and 30CrMnSiA steel butt joints were carried out with different beam currents. Microstructures and chemical compositions of typical zones were analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties of the joints were evaluated by tensile strength tests. Besides, nanoindentation tests were carried out to compare the brittleness of the reaction layer and other typical microstructures. The results illustrated that the reaction layer at the interface between fusion zone (FZ) and TZM alloy was the weak position of the joint, which was divided into Fe₂Mo layer and a mixture layer of Fe₂Mo and α-Fe phases. As the beam current increased, the thickness of the Fe₂Mo layer decreased, which resulted in the increasing of the tensile strength of the joints. When the beam current exceeded 24 mA, the formation of the joint was poor with a low tensile strength. When the beam current was 24 mA, the joint presented the highest strength of 191.3 MPa and the joint fractured along the Fe₂Mo layer near the TZM alloy side with a brittle fracture mode.